In many areas, a gas is used as a processing agent to treat a material. Examples of this include water treatment, waste water treatment and chemical oxidation (i.e. bleaching).
Accordingly, various different sensors have been developed to measure the level of a gas in a liquid. These include ORP sensors, photometric devices and electrolytic devices.
Ozone is used in various applications in industry and accordingly, sensors for detecting the concentration of ozone have been developed. Typically, these operate by passing ultraviolet light through a fluid stream and measuring the ultraviolet light which is received on a detector. Another type of gas sensor is disclosed in U.S. Pat. No. 5,167,927 to Karlson. Karlson discloses a monitor which measures the heat energy which is released when a gas, eg. ozone, is catalytically converted to a different compound (eg. oxygen).
One example of the use of ozone is to purify water for drinking by passing ozone through the water to kill microorganism contaminants such as bacteria present in the water. Various processes to treat water have been developed using combinations of filtration and ozonation.
For example, U.S. Pat. No. 5,683,576 to Olsen describes an apparatus for treating contaminated water by passing ozone through the water. In the system disclosed by Olsen, an ozone containing gas is passed through the water to be treated, until the instantaneous concentration of ozone in the head space above the water being treated reaches a predetermined level. Then, the flow of ozone through the water continues for a predetermined period of time.
The amount of ozone which must be passed through the water to purify it to any particular state will vary depending upon the initial quality of water to be treated. For example, untreated well or lake water may require a higher degree of purification than treated city water which has previously been treated to some degree.
One disadvantage of Olsen is that it can not be reliable used with such disparate types of water supply. Olsen does not monitor the total amount of ozone which passes through the water unreacted. Thus, the actual degree of treatment of the water is not measured. The system is designed only to ensure that a predetermined minimum amount of ozone passes through the system unreacted. The system makes the assumption that once the concentration of ozone reaches the predetermined level, that it does not subsequently drop below that level, or rise above that level. Further, it assumes that once the water to be treated has been exposed to the preset ozone concentration for a predetermined time that the water is suitable for use. However, depending on the degree of contamination of the water to be treated, the time required to treat the material will vary.
In Olsen, the amount of unreacted ozone passing through the system prior to the time when the instantaneous concentration reaches the predetermined level is not measured. Further, the amount of unreacted ozone passing through the system measured during the predetermined amount of time after the predetermined instantaneous concentration is reached is not measured. Thus, the actual degree of treatment of the water is not measured.
Another disadvantage of the method of Olsen is that, in some applications, it is desirable to monitor the degree of treatment of material as it is being oxidized.
Accordingly, there is a need for a method and apparatus to accurately measure the amount of treatment to which water has been subjected by passing ozone through the water. Further, there is a need to do so on a cost effective scale.